A road pavement usually is of a three-layer pavement construction comprising a roadbed, a sub-base and an asphalt mixture layer as shown in FIG. 1, wherein the sub-base is provided on a compacted roadbed and comprises aggregates such as sand and crushed rocks added with a stabilizing agent such as a cement or petroleum asphalt emulsion, the sub-base being compacted after the stabilizing agent is added to the aggregates and being comprised of a lower layer and an upper layer for providing a required strength. The asphalt mixture layer comprises a base layer and a surface layer and is provided and compacted over the sub-base. In general, the term pavement is used to designate “a sub-base and an asphalt mixture layer”, and the asphalt mixture includes particles of aggregate such as sand or crushed rocks, an asphalt which serves as a binder and stone powders (filler) comprised of limestone powders adapted to fill spaces in the particles of the aggregate .
As shown in FIG. 1, an asphalt mixture layer is formed in a two-layer construction comprising a base layer and a surface layer to be a water impermeable pavement typically comprised of a dense graded asphalt mixture layer having a void ratio of approximately 4%, the void ratio being defined as the volumetric ratio of voids in the mixture layer. In addition to such water impermeable pavement, a drainable pavement and a water permeable pavement having a void ratio of approximately 20% have been known. It should be noted however that a water permeable pavement allows water to pass to the roadbed possibly resulting in an adverse effect even the roadbed is caused to be weakened, so that such a water permeable pavement has not usually been adopted for the pavement of a heavy traffic road but has generally been adopted for pavements in side-walks or relatively light traffic roads.
Meanwhile, it has been known that paved roads which are subjected to heavy traffic due to busy vehicle transportation have problems of road surface deformation due to a road surface wear caused by being subjected to serious weather conditions for a prolonged time or due to a so-called “rutting” phenomenon, as well as road cracking due to deterioration, with the result that traffic safety is disturbed because rain water or thaw water may be trapped on the road surface causing a water splash or hydroplaning phenomenon, so that such road needs to be renewing of pavement through a repair work such as an asphalt repaving or patching.
A drainable pavement, generally referred as “an open graded asphalt mixture layer”, has been developed in view of such problems, and comprises, as shown in FIG. 2, an asphalt layer construction including water impermeable base layer of an asphalt mixture disposed on the roadbed and a water permeable surface layer provided on the base layer, whereby rain water is guided and drained to drainage gutters or the like, not shown. To improve drainage capability, it has been proposed to increase the void ratio. However, the void ratio should not be increased at random because too large void ratio may cause problems such as strength reduction of a road surface layer itself, or viscosity degradation of the asphalt binder by softening asphalt binder based on increasing the temperature of a road surface layer with ambient temperature rise, and abruption of aggregates by driven vehicles based on such viscosity degradation.
Although the thickness of a pavement is determined by the strength of the roadbed (CRB value) and the traffic volume (N value) from the durability point of view, each thickness of a sub-base and an asphalt mixture layer is usually designed to be from two to three times in length of the maximum diameter of aggregates mixed therein. The maximum diameter of aggregates mixed into a sub-base is generally around 40 mm, thus the thickness of the sub-base is designed to be adapted to be around 100 to 120mm. Furthermore, the maximum diameter of aggregates mixed into an asphalt mixture layer is usually around 20 mm, thus each thickness of the base layer and the surface layer comprising the asphalt mixture layer is designed to be adapted to be around 40 to 50 mm, consequently the total thickness of the asphalt mixture layer may be around 80 to 100 mm.
The size of aggregate is referred as a particle size, and the mixture condition of these particles of aggregate which can be classified using screening device having a variety of screen meshes is referred as a particle size distribution. The particle size distributions of aggregates mixed into a dense graded, water impermeable asphalt mixture layer and into an open graded, water permeable asphalt mixture layer are obviously different. FIG. 3 and FIG. 4 show the respective particle size distributions. Each graph shows that the horizontal axis indicates the screen meshes, and the vertical axis indicates the weight percent of the particles of aggregate which have passed through each screen mesh (percentage passing by weight). Because aggregates may be typically grouped on the basis of 5 mm in diameter, particles of aggregate greater than 5 mm in diameter are called as coarse aggregates, and particles of aggregate smaller than 5 mm in diameter are called as fine aggregates. The coarse aggregates may also be grouped in more detailed manner, such as medium aggregates comprised of particles of aggregate greater than 5 mm and less than 13 mm in diameter, and coarse aggregates comprised of particles of aggregate greater than 13 mm and less than 20 mm in diameter. Since aggregates included in an asphalt mixture layer may be screened to be classified into two or three groups in many cases to be reused for recycling, the classification method as described above is also adopted here as a matter of convenience.
Referring to FIG. 3, it can be seen that particles of aggregates having particle size greater than 0.075 mm and less than 20 mm in diameter distribute continuously. This shows that the particle size distribution is such that the aggregates can be packed with a highest density, and the particle size distribution may be recognized as a continuous particle size distribution or particle size continuity, which is generally referred as “a dense graded asphalt mixture layer” and is of a water impermeable characteristics. FIG. 4 shows a particle size distribution of aggregates in which a group of medium size aggregates have been removed from materials including for example three groups of aggregates, such as a first group of fine size aggregates, a second group of medium size aggregates and a third group of coarse size aggregates. If coarse aggregates greater than 5 mm in diameter have been removed from the particles of aggregate classified into two groups in accordance with different particle sizes not shown here, the particle size distribution shows a distribution concentrated in particles of aggregate less than 5 mm in diameter. In both cases, particle size distribution graphs indicate particle size distributions with gap or discontinuity in particle size distributions neither continuous particle size distribution nor particle size continuity. However, where medium aggregates have been removed from the particles of aggregate classified into three groups in accordance with different particle sizes, particles of aggregate comprising fine aggregates fill up densely spaces in the particles of aggregate comprising coarse aggregates, due to a weight percent of coarse aggregates smaller than that, i.e. around 30%, of fine aggregates. In case of two groups classified into fine aggregates and coarse aggregates, asphalt mixture includes only particles of aggregate comprising fine aggregates because particles of aggregate comprising coarse aggregates have been removed. In each case, where fresh asphalt or the like has been added to remainder of particles of aggregate which medium aggregates of the three groups or coarse aggregates of the two groups have been removed to provide a renewed asphalt mixture layer, the pavement may also be “a dense graded, water impermeable asphalt mixture layer” having a void ratio of around 4%. On the other hand, where fresh asphalt or the like has been added to particles of aggregate comprising medium aggregates removed from the three groups or to particles of aggregate comprising coarse aggregates removed from the two groups to provide a renewed asphalt mixture layer, the pavement may also be “an open graded, water permeable asphalt mixture layer” having many voids therein caused by not containing fine aggregates less than 5 mm in diameter. These two types of asphalt mixture layer are also referred to as a dense graded asphalt mixture layer and a porous asphalt mixture layer, respectively.
There are two kinds of asphalt (binder) used as an aggregates binder, one is crude asphalt called as strait asphalt which is unmodified, the other is modified asphalt which modifying agent such as rubber or resin has been added to improve viscosity, as seen in the relation between temperature and viscosity shown in FIG. 5, an asphalt mixture comprised of asphalt and aggregates will be divided into aggregates without damages and liquid asphalt when the viscosity of any kinds of asphalt diminishes around 180 degrees centigrade. That is, aggregates covered by asphalt may disaggregate to be particles. Meanwhile, the viscosity of asphalt increases under a temperature less than 100 degrees centigrade, whereby aggregates covered by asphalt will begin to re-aggregate, and then the asphalt mixture comprised of aggregates and asphalt will completely solidify at normal ambient temperatures. In this state, such asphalt mixture is also called as an asphalt concrete. According to the simulation shown in FIG. 6, the critical asphalt temperature for disaggregating aggregates covered by asphalt is around 120 degrees centigrade.
So far, although an asphalt mixture layer of typical three-layer construction pavement has been described, as stated above, an asphalt mixture layer comprising road pavement, for a prolonged time, has problems of road surface deformation such as so-called “rutting” phenomenon due to road surface wear caused by being subjected to busy vehicle transportation and due to fluidization of the asphalt mixture layer due to softening of asphalt (binder) in accordance with a rising of an ambient temperature caused by being subjected to serious weather conditions, as well as road cracking due to deterioration. An on-site recycling pavement construction method for an existing pavement typically implies a construction method for a surface layer of a two-layer asphalt construction comprised of a surface layer and a base layer. It should be noted however that the present invention has been conceived a concept as an on-site recycling pavement construction method of an asphalt mixture layer including a construction method for a surface layer of an asphalt mixture layer because road surface deterioration due to road surface wear and so-called “rutting” phenomenon may extend to a base layer. Hereinafter, the invention will be described in comparison with the prior arts related to on-site recycling pavement construction methods.
In surface pavement work for various roads or airport runways, various repair or repaving construction processes have been adopted and these processes have included simple repair process and surface and/or base layer renewing process which have been chosen depending on applications. Meanwhile, recycling methods for recycling pavement materials generated by construction have been widely adopted since the enactment in Japan of Recycle Law in 1991, for example, from the viewpoint of saving pavement materials consumed in maintaining and repairing pavement of a road having a significantly large length, and, for preventing pavement materials from being discarded as industrial wastes. Such processes are usually implemented by transporting/carrying pavement materials removed from a road surface under construction to a remote processing plant generally located away from a worksite using a construction vehicle, whereby the once-used pavement materials are regenerated in the plant and then transferred back to the worksite for a second use. This is commonly referred as a “plant regeneration pavement process”. Typically, a pavement renewal process is carried out, with or without the plant regeneration process combined therewith depending on the condition of road, by applying heat to a surface portion of an asphalt mixture layer to perform an on-site renewal, or by scarifying asphalt mixture and mixing with pavement sub-base materials. The former is ordinarily referred as an on-site road surface recycling process, while the latter is referred as an on-site sub-base recycling process. The present invention relates to the one which have been conceived based on the former process.
(Nonpatent literature 1): “Pavement Recycling Handbook” (Japan Road Association Aggregates Corporation)
Asphalt is comprised of particulate ingredient called as asphalting, and oil ingredient called as methane, and the content of methane tends to be decreases as the pavement is aged with the result that the asphalt is made harder and less viscous due to an increase in relative amount of asphaltene to methane. Furthermore, aggregates mixed in the asphalt mixture layer may be subjected to abrasion and breakage. Therefore, where materials of asphalt mixture removed from a road pavement are reused as old or once-used materials, it is necessary to ensure that the predetermined specifications shown in Table 1 are achieved by adding a rejuvenating agent such as softener, and, fresh asphalt mixture (new materials) and/or fresh asphalt as modifying agent, which are added in an amount appropriately metered in relation to the old or once-used materials. From an efficiency point of view, it is difficult to incorporate such blending step into a continuous on-site recycling process of an asphalt mixture layer of a pavement, so that the blending step is generally carried out as an off-line process wherein fixed or mobile plants are utilized to produce regenerated materials of asphalt mixture having predetermined specifications which are then transported back to the worksite. Although the plant regeneration pavement process has been established as a process for ensuring predetermined specifications, it is evident that technical and social issues caused by a loss of efficiency of application and disruption of traffic due to of the transportation from and to the worksite by construction vehicles due to the facts that the old materials must be carried back and forth between a plant and a worksite with the method. To improve such issues, mobile plant construction methods and plant vehicles have been also proposed.
(Patent literature 1): Japanese Patent Laid-Open Publication NO. 2002-079136A
(Patent literature 2): Japanese Patent Laid-Open Publication NO. 2004-011406A
(Patent literature 3): Japanese Patent Laid-Open Publication NO. H 7-003715A
TABLE 1Tested ItemsTypical ValuesPenetration value 1/10 mm40 and up(25° C.)Softening point° C.80.0 and upDuctility (15)cm50 and upFiring point° C.260 and upThin film oven mass%0.6 and underrate of changeThin film oven%65 and upresidual penetrationToughness (25° C.)N · m (kgf · cm)20 (200) and upTenacity (25° C.)N · m (kgf · cm)15 (150) and upViscosity (60° C.)Pa · s (Poise)20,000 (200,000) and up(1) Density (at 15° C.) should be written on a test sheet.(2) Optimal mixture temperature range and optimal compaction temperature range should be written on a test sheet.
The so-called on-site road surface recycling process as described above is typically performed on the road by a sequence of process steps of applying heat to the road surface of an asphalt mixture layer by a road heater for recycling to be softened, scarifying and loosening materials of thus softened asphalt mixture layer, adding a rejuvenating agent such as softener or the like to the materials to be mixed therewith, optionally adding fresh asphalt mixture (new materials) and/or fresh asphalt as modifying agent and mixing them again together to produce a regenerated asphalt mixture, finally spreading and compacting the regenerated asphalt mixture by means of a screed or the like. There are two construction methods used for the purpose, one being a process referred as a remixing method wherein a rejuvenating agent and fresh asphalt mixture (new materials) and/or fresh asphalt may be added to the old materials in order to improve viscosity of asphalt materials and the binding force of the asphalt materials in the old materials and mixed them together to produce a one-layer construction of a renewed asphalt mixture layer, the other being a process referred as a repaving method, which can be adopted where it is not necessary to renew an asphalt mixture layer to improve quality, or where only minor improvements are needed, for producing a renewed asphalt mixture layer of a two-layer construction comprised of an old material layer and a new material layer paved on the old material layer. There have been proposed a number of approaches for improving properties of the regenerated asphalt mixture used for an on-site road surface recycling method. An example may include a surface recycling process performed by steps of forming grooves in advance along the road in a transverse, width direction by cutting the road pavement at the opposite sides of the road and removing materials of asphalt mixture generated by cutting, and then scarifying and loosening an existing road surface layer between the grooves, and spreading and compacting the scarified and loosened materials of the road surface layer back over the entire road surface throughout the width, and finally adding the same amount of new materials as that removed for forming the grooves in the opposite sides in order to adjust a height of the road, another type of recycling method of forming a road surface layer from an existing open graded, water permeable asphalt mixture layer being the one performed by steps of removing a part of the surface layer from materials of an existing asphalt mixture layer, and instead adding new materials so that spaces in the aggregates may be remained. In this regard, however, anyone of known on-site recycling methods does not need to contemplate recycling materials of an existing asphalt mixture as raw materials on the road by reusing and blending all or a part of aggregates in different diameter including the existing asphalt mixture. In the known methods, therefore, there have been no idea of restoring regenerated aggregates to be used as raw materials on the road, and blending the regenerated aggregates to reuse them on the road. Furthermore, known construction methods are not able to assure particle size distributions as described in FIG. 3 and FIG. 4, because a sequence of construction steps on the road are not based on screening aggregates included in an existing asphalt mixture to classify into multiple particle size distributions by a screening device or the like, and measuring them by a measuring device, and then blending them by a blending device to produce regenerated materials of asphalt mixture. In other words, it is impossible to assure a variety of predetermined performances completely because their steps are not incorporated into the sequence of construction steps. AR2000, which is manufactured and distributed by the applicant; is a state-of-the-art construction method that allows continuous recycling of an asphalt mixture of pavement on the road while the motor-driven vehicle system moves under automatic control at an average speed of 4 to 5 m/minute. However, a variety of predetermined specifications can not be ensured with even this system which operates similarly to known construction methods.
(Nonpatent literature 2): “Pavement Recycling Handbook” (Japan Road Association Aggregates Corporation)
(Patent literature 4): Japanese Patent Laid-Open Publication NO. 2004-124549
(Patent literature 5): Japanese Patent Laid-Open Publication NO. 2001-262509
Although a variety of construction methods relating to recycling of asphalt mixture (old materials) on the road have been suggested other than those described above including component technology, anyone of these methods is also unable to ensure a variety of predetermined performances completely, because they are not based on incorporating steps of screening aggregates in different diameter mixed into materials of asphalt mixture (old materials) to classify into multiple particle size distributions, measure them, and blending the particles of aggregate included in the materials of asphalt mixture as regenerated materials, into a sequence of construction steps on the road.
(Patent literature 6): Japanese Patent NO. 3293626
(Patent literature 7): Japanese Patent NO. 3380590
(Patent literature 8): Japanese Patent Laid-Open Publication NO. H11-117221
(Patent literature 9): Japanese Patent Laid-Open Publication NO. 2002-061140
Because any known on-site recycling pavement construction methods of an existing pavement including a step of performing a recycling plant process of materials of asphalt mixture (old materials) therein, require additional steps of process for transporting the old materials and the regenerated materials of asphalt mixture to and from between a recycling plant and a worksite as described above, it is difficult to avoid increasing green house gasses due to incoming and outgoing vehicles and due to traffic jams caused by road closure for prolonged time, and also prolonging of construction term and increasing of construction cost in accordance with reduction of construction efficiency. Furthermore, it is possible to take place insufficient compaction, low density and decreased adhesive force with aggregates caused by decreasing a temperature of materials of asphalt mixture until their arrival to a worksite because a recycling plant is usually located away from the worksite when a renewed asphalt mixture layer has been produced.
Meanwhile, known on-site recycling pavement construction methods as described above enable one to add a rejuvenating agent and new materials to old materials, and mix them together to produce a regenerated asphalt mixture on the road, and then spread and compact the regenerated asphalt mixture. However, a system has not been developed so far to enable one to apply heat to the asphalt mixture layer to be softened, scarify and loosen materials of thus softened asphalt mixture layer to divide the materials into particles under a temperature wherein re-aggregation of the loosened particulate materials can be prevented to thereby provide particles of the divided materials of the asphalt mixture, screen the particles of the divided materials of the asphalt mixture to classify into a plurality of groups of different particle size distributions in accordance with particle sizes, blend continuously particles of different particle sizes in the plurality of groups to provide a regenerated asphalt mixture which meets predetermined specifications or performances on the road as carrying out in a recycling plant, mix uniformly the regenerated asphalt mixture, and then spread and compact the uniformly mixed, regenerated asphalt mixture over the road surface to provide a renewed asphalt mixture layer over the road surface. There are premises enabling these developments by resolving technical problems which have been proposed in a patent literature of Japanese Patent NO. 3466621 adopted in AR2000 as described above. The techniques shown in the patent literature enable materials in depth of 40 to 50 mm of an asphalt mixture layer to heat up around 80 degrees Centigrade in a short period of time while keeping the surface temperature of the existing asphalt mixture layer at around 230 degrees Centigrade, by using a heating method and device for spraying and circulating a blast of hot air at around 600 degrees Centigrade to a road surface of an asphalt mixture layer with a motor-driven vehicle system moved along the road surface, whereby the asphalt mixture layer from the surface to the depth of 40 to 50 mm of an existing pavement may be scarified and loosened materials of an asphalt mixture layer to divide the materials including asphalt-coated-aggregates into particles under a temperature wherein re-aggregation of the loosened particulate materials can be prevented, to thereby provide particles of the divided materials of the asphalt mixture without damages.
(Patent literature 10): Japanese Patent NO. 3466632
So far, it is impossible to alter the functions or aspect of the asphalt mixture layer by incorporating the modification of particle size distribution comprising aggregates into a sequence of known on-site construction steps, with the result that such particle size distribution comprising aggregates have not been able to be converted into raw materials for recycling by reprocessing materials of asphalt mixture at a worksite in the prior arts. In other words, it is obvious that an open graded, water permeable asphalt mixture layer cannot be formed continuously on the road by reusing raw materials regenerated from an existing dense graded, water impermeable asphalt mixture layer at a worksite in the prior arts. More particularly, there has been no idea related to incorporating a reprocess capable of blending particle size distribution comprising aggregates included in an existing asphalt mixture layer into a sequence of construction steps. Patent literature 3 describes, “A road pavement vehicle wherein includes at least means for screening and classifying crushed asphalt-concrete scrap and/or cement-concrete scrap, means for mixing, measuring and feeding the screened and classified asphalt-concrete scrap and/or cement-concrete scrap as regenerated aggregates in different diameters with specified ratios thereof, means for mixing, measuring and feeding fresh aggregates in different diameters with specified ratios, means for measuring and feeding fresh asphalt, and then means for mixing said regenerated aggregates, said fresh aggregates and said fresh asphalt with applying heat thereto by means for heating.” Although this is a vehicle-type-plant that provides a hopper, a screener and a mixer equipped on a frame of a carriage which can be placed near a construction worksite, and can be blended old materials crushed mechanically to meet desired specifications or performances thereof, this is not a vehicle configured a portion of a system that is incorporated a step for regenerating old materials continuously on the road into a sequence of construction steps. In other words, this is a vehicle of a type of mobile plants. It is obvious that such vehicle is not based on the concept of producing raw materials from aggregates included in old materials of an existing asphalt mixture layer to blend and reuse them on the road. More particularly, this is not a vehicle which is able to apply heat to old materials of an existing asphalt mixture layer to be soften, scarify and loosen the old materials to divide the old materials into particles of aggregate under a temperature wherein re-aggregation of the scarified and loosened old materials can be prevented, to thereby provide particles of the divided old materials of the asphalt mixture, screen the particles of aggregate to classify into multiple particle size distributions to produce raw materials, incorporate a step of blending process for them into a sequence of construction steps on the road by measuring the weight thereof as a reprocessing in an asphalt recycling plant, and then form continuously a regenerated asphalt mixture layer of a pavement on the road.